In the design of optimum lasers, especially high power lasers, certain physical requirements have been recognized as desirable. These include maximum active volume, maximum beam cross-sectional area, and maximum surface area of the laser material available for cooling. The configuration of the laser should also align thermal profiles along the laser axis, and should suppress parasitic modes actively or passively.
Prior approaches to these desiderata have included zig-zag and stack configurations. In the former, the beam executes a zig-zag path, e.g. sawtooth or square, while a particular form of a stack configuration is the ring laser in which the light beam successively longitudinally traverses laser amplifiers arranged substantially in a ring. A common feature of the family of laser designs embodying zig-zag and stack configurations is that pumping is distributed longitudinally, either continuously or discretely. For high power applications, this feature has several disadvantages and limitations: pumping is non-uniform and inefficient, the devices tend to be physically large, and cooling is generally inefficient.
Some stack configurations, such as a nest of layers inclined to the incident beam, do allow a good circulation of cooling gas about the layers but still exhibit several disadvantages. In particular, pumping is non-uniform and inefficient, and cooling, since it is by gas only, requires extremely low temperature gases to operate.